In an attempt to figure out just how Barnaby is managing to average more than 50mpg in his 2.0-litre diesel Octavia – when I consistently get high 40s from my Volkswagen Golf 1.6 TDI – I recently borrowed it for a week.

First, there’s the obvious: the Octavia has six forward gears, whereas the Golf has five and therefore revs more highly on the motorway, which is where I spend most of my commute.

It took me a few days to realise what other factor plays a part: you don’t need to work the Skoda’s engine anywhere near as hard as the VW’s to make decent progress. Unsurprisingly, the Octavia’s motor has more power and more torque, and is more relaxed in all situations.

The official economy figures suggest that the Golf should be bettering the Octavia by around 5mpg, but that’s plainly not what’s happening – further proof that the shrinking of diesel (and petrol) engines in an effort to reduce official CO2 emissions doesn’t always have the desired effect on real-world fuel economy.

I’m dying to see what sort of results our True MPG team will get from the Mondeo when Ford starts to sell it with the 1.0-litre Ecoboost petrol engine.